1. Field of the Invention
The present invention relates to a battery which comprises an electricity generator element. Particularly, it relates to an electricity generator element in which an electricity collector is kept in a laminated state. The electricity collector is coated with an active material on the surface, and a plurality of tabs for taking out a generated current project from the electricity collector. More particularly, it relates to the reduction of the space required for gathering and integrating the tabs so that the resulting battery can be compact and exhibit high performance.
2. Description of the Related Art
The following batteries are known to be made by bonding current-taking-out tabs to an electricity collector which constitutes an electrode: a laminated square-shaped battery in which a plurality of square-shaped electricity collectors are laminated; a spiral lithium battery or a cylinder-shaped Ni--Cd battery in which a band-shaped electricity collector is wound. For instance, the spiral lithium battery is constructed as follows: a cathode employed by the spiral lithium battery is made by coating a band-shaped electricity collector with a cathode active material; then, a plurality of current-taking-out tabs are bonded to a part of the resulting cathode; further, a band-shaped anode is superimposed on the thus prepared cathode by way of a separator, and they are wound integrally in a spiral manner; and the thus prepared spiral electricity generator element is finally accommodated in a cylinder-shaped battery container. Concerning the method for bonding the tabs to the cathode(or to the electrode in general), the ultrasonic welding, the resistance welding and the crimping are employed.
In a small-sized battery whose current capacity is about 1 Ah, a tab is made by using a metallic foil which has a thickness of a couple dozens of micrometers and a width of a few millimeters. The tab is attached to each of the cathode and anode in a quantity of 1 at least. A current of about a couple of amperes flows in each of the tabs when the small-sized battery is discharged or recharged. The tab can be attached at a leading end of the wound band-shaped electrodes, or at a terminal end thereof, or even at a central portion thereof.
A relatively large-sized battery whose current capacity is, for example, from a couple dozens to a couple hundreds of ampere-hours fundamentally has the same construction as that of the small-sized battery. Since, a band-shaped electrode is formed as a long and continuous substance and has a large surface area, there is a great difference in that it is necessary to attach a plurality of tabs entirely over the electrodes at predetermined intervals so that the discharge and recharge take place entirely over the electrodes without loss, and evenly. When the large-sized battery is provided with a plurality of the tabs, the bonding portions of the tabs have a complicated structure, for instance, as illustrated in FIG. 21. In the large-sized battery of the drawing, a band-shaped cathode "A" and a band-shaped anode "B" are wound by way of separators "C1" and "C2", respectively, as illustrated in FIG. 22. Accordingly, an electricity generator element "D" is made by superimposing the cathode "A" and the anode "B" in a spiral manner. The electricity generator element "D" is then accommodated in a battery container "E" as illustrated in FIG. 21. The cathode "A", and the anode "B" are provided with a couple dozens of tabs "F" as illustrated in FIG. 22. In many cases, the thickness of the tabs "F" is dependent on the thickness of the cathode or anode active material. For example, the thickness of the tabs "F" is from a couple dozens to a few hundreds of micrometers. Generally speaking, the tabs "F" are formed as a thin plate shape at least at the attached portion, and are formed as a complicated ribbon-like shape at the portion projecting from the electricity collector (i.e., the cathode "A" and the anode "B", or the electricity generator element "D").
When winding a band-shaped electrode which is provided with a plurality of the tabs at equal intervals, however, the tabs are projected extremely randomly as illustrated in FIG. 5, thereby making it difficult to bond them together to be integrated. Accordingly, one may think of displacing the tabs by a small distance back and forth from the positions which are disposed at equal intervals. By thus displacing the tabs, it is possible, in calculation, to project the tabs from the aligned positions as illustrated in FIG. 23. When the projected tabs are aligned, it is easy to bond the aligned tabs integrally to form a complete terminal "G" as illustrated in FIG. 24. In actual winding processes, however, the tabs cannot be aligned in the second half of the winding processes, though they can be aligned in the first half of the winding processes. The disadvantage results from the fact that the band-shaped electrode is tightened by winding to differently wound states in every turn of winding in the second half of the winding processes. Thus, it is actually difficult to align the tabs. In the actual winding processes, the positions of the tabs fluctuate in a range of about 45 degrees of sector angle. A space of from about 20 to 30 mm in height is required to integrate the thus disaligned tabs.
Whilst, there are indexes for rating the performance of a battery, such as the energy per unit weight (Wh/g) and the energy per unit volume (Wh/cm.sup.3). When a battery is limited in terms of the overall size, the extra spaces, such as the space for bonding and integrating the tabs, should be removed as much as possible in order to upgrade the energy-density indexes. When the tabs are connected by conventional techniques, the tabs are connected complicatedly to take up extra space, thereby reducing the area of electrodes. Consequently, it is difficult to reduce the extra spaces and to provide high performance for batteries.
The same problems exist in the laminated square-shaped battery. FIG. 25 illustrates the construction of the laminated square-shaped battery. In the battery, the electrodes, namely, a cathode "A" and an anode "B" are formed in a square shape. A number of the cathodes "A" and anodes "B" are laminated in layers by way of separators "C" to make an electricity generator element "D". A plurality of tabs "F" are projected from one of the sides of the cathodes "A" and anodes "B", and are superimposed lamellarly. When the thus laminated tabs "F" are integrated, the tabs "F" are bonded at the leading ends "H" as illustrated in FIG. 27. Although the portions "I" of the tabs "F", which project from the electricity collector, are not formed as complicatedly as the ribbon-like shape in the spiral lithium battery shown in FIG. 21, they require a space in proportion to the number of the laminations of the cathodes "A" and anodes "B".